1. Field of the Invention
The invention relates to a motor vehicle control system having at least two separate control units, which are connected with one another by way of a bus system, and a method for controlling motor vehicle components by means of the motor vehicle control system.
2. The Prior Art
It is generally and previously known to provide a combination of control devices in vehicles, whereby a separate control device is provided for individual functions (engine control, transmission control, ABS, etc.), in each instance. In this connection, the control devices are connected by way of a bus system and can communicate with one another, exchange data, etc. The constant expansion of functionality has the result, particularly in the case of complex control devices, such as the engine control device, of rapid changes in the control device hardware, whereby the memory space, I/O ports, and computer performance are expanded. As soon as control devices and software are ready for series production, their capacity limits are already reached. Time-consuming and cost-intensive adaptation of the control devices to the increased demand for memory space and computing speed, in each instance, are the result.
A method for operating a control device for a motor vehicle, in which two control units are connected by way of a data bus, is previously known from DE 197 50 026 A1. If it is determined, during operation of the control units, that one of the control devices has reached its performance limit, control device functions are temporarily transferred to the second control device and performed there. In this connection, the program code of the function is transmitted to this control device, or a function implemented in dual manner, that is already present on the second control device, is utilized. It is a disadvantage with this method of procedure that the entire program code has to be transmitted once, or that the functions have to be implemented in the control devices in dual manner. This results in additional memory requirements and is impossible for complex functions. Furthermore, a significant effort has to be made for temporarily transferring the functions. The capacity of the control device to which they are transferred must be checked, the program structures are switched over to the control device to which the function is being delegated, since a new function has to be linked. This is impossible, in particular, for time-critical and safety-relevant functions.
The use of a client/server architecture on a vehicle control device combination is previously known from DE 197 48 536 C2. Here, the individual application functions are described independent of the devices and addressed by way of a communication interface. Any communication between the processes therefore generates a data exchange, which must take place by way of the bus system. The individual application functions can therefore be implemented only once, in order to save space, and are available to several requesters. The method requires an additional level (function monitor level) that functions as a central control unit as well as a central memory for the individual systems (clients/servers). It is a problem, in this connection, that the individual functions can be called up by several requesters at the same time, and that the response times are lengthened due to the sequential processing. Use under real-time conditions, such as for an engine control device, for example, is therefore problematic.
The significant advantage of the client/server architecture lies in the central management of the functions, whereby these only have to be implemented once for the applications, in each instance. The individual vehicle control devices, e.g. engine control device, transmission control device, ABS control device, have only very few functions in common, however, so that the construction of a client/server architecture for common use of the functions does not produce any decisive advantages.